Steam is used in commercial kitchens in appliances of various types. Steamers for cooking vegetables and fish for example, or for re-therming food products to serving temperature, are well known in the industry. Recently, convection-steam and convection-steam-microwave ovens have become commercially available for baking and roasting applications. Steam has also been used, at least experimentally, in ware wash machines for heating ware and hydrating soil.
There are two conventional approaches for locally producing steam in an appliance: immersion boiling and open pan boiling. In immersion boiling (alternatively referred to as an ‘immersion steam generator’) a heating element (usually an electrical heating element, although a gas heating element is also contemplated) is immersed in a vat of water. The heating element heats the water, which boils to produce steam. Immersion steam generators may be used to produce large amounts of steam and are commercially attractive as their operating pressures are low. However, any metal ions in the water (either light ions, such as sodium or potassium, or heavy ions, such as calcium, iron or manganese) are left behind and are usually found deposited on the vat wall, the heating element or both. These deposits (alternatively referred to as ‘scale deposits’) may be sizable (up to 2 grams per gallon of water to steam).
Deposits in immersion steam generators are usually managed or treated by regularly flushing the vat with an acid solution to dissolve the deposits or by treating the incoming water to reduce or eliminate ions. The vat must be serviced often to properly manage the deposits. However, using an acid solution to service the immersion steam generator is inconvenient and is thus generally neglected, causing deposit buildup, which in turn reduce the life span of the immersion steam generator. Treating the water is expensive as compared to servicing the steam generator and, depending on the treatment method chosen, may also require servicing.
Open pan boiling (alternatively referred to as ‘pan boiling systems’) is more often used in less expensive steamers. Pan boiling systems include a shallow pan of water in a heated iron bottom (or other metal bottom) of the system. The heat is provided or supplied from below the system. This style of steam generation is often preferred over immersion steam generation as the heat, and the resultant steam, is only produced when needed. That is immersion steam generators usually operate continuously due to their long heat up time. However, currently available pan boiling systems have low steam production capacity and are susceptible to the same metal ion deposit limitations as immersion steam generators, thus requiring similar scale deposit management.
Monotube steam generators are also commercially available to produce steam. However, such known monotube steam generators are sized to reduce material consumption and minimize the diameter to accommodate fluid flow.
It would, therefore, be desirable to design a heating unit that reduces scale deposit buildup. It would further be desirable to produce steam using such a heating unit that reduces scale deposit buildup.